Echo canceller and method of echo cancellation using an NLMS algorithm

摘要

An echo canceller and a method of echo cancellation using an NLMS algorithm. The NLMS algorithm alternates adaptation between a slow mode, aggressive mode, and inhibition mode, according to the status of the echo canceller. This implementation requires no correlation information. This implementation is simple and not very time consuming. During initial conversation, the NLMS algorithm is in an aggressive mode to ensure fast convergence. After convergence, the NLMS algorithm switches to a slow mode for lower residual echo return. Whenever an abrupt increase of residual echo caused by either double talk or echo path change is detected, the current adaptive filter coefficients are retained and then updated in the aggressive mode. The decision as to which echo estimation (the response of the retained filter or the response of the aggressively adapted filter) is subtracted from the reference echo for echo cancellation within a short detection delay period is determined according to the Geigel algorithm. After the short delay, the NLMS algorithm makes a more accurate determination of double talk or echo path occurrence. If double talk is detected according to the more accurate determination, then the retained filter taps are applied to yield the residual echo and the inhibition mode is chosen and maintained until the error signal again decreases to the pre-changed value range. Otherwise, the aggressively adapted filter taps are applied to yield the residual echo and the system switches to aggressive mode adaptation until a new convergence is achieved. This implementation also has high convergence rate, high stability, and a small detection delay.